This is probably related to the Node 8: 'yarn check' gives error after precompile topic.
When I type a character in the search field (‘zoeken’ in the screenshot) the web-app disappears and I only see the background. F5 brings everything back. Not every character gives these errors. e.g. ‘h’ and ‘1’ does, ‘f’ and ‘5’ does not.
The following errors are in Firefox’ web development debugger:
Running v2.4.3 on Debian 9